1. Field of the Invention
The present invention relates to a sialon based composite having excellent mechanical strength and fracture toughness and a method of manufacturing the same.
2. Description of the Related Art
Two sialons are generally known: .beta.-sialon which is represented by formula Si.sub.6-z Al.sub.z O.sub.z N.sub.8-z (wherein 0&lt;z.ltoreq.4.2) and is obtained by adding Al.sub.2 O.sub.3, AlN, SiO.sub.2, and the like to Si.sub.3 N.sub.4, and heating the resultant mixture to solid-dissolve these additives in Si.sub.3 N.sub.4 (that is, to make a solid-solution), and .alpha.-sialon which is represented by formula Mx(Si,Al).sub.12 (O,N).sub.16 (wherein 0&lt;x.ltoreq.2; M represents at least one element selected from the group consisting of Li, Na, Ca, Mg, Y, and rare-earth elements) and in which a metal is soliddissolved in the crystal lattice of Si.sub.3 N.sub.4. A sialon sintered body is excellent in heat resistance and oxidation resistance, and its strength is not degraded at high temperatures exceeding 1,300.degree. C. In addition, even if a sialon sintered body is oxidized at a high temperature, its properties are not impaired. Therefore, sialon sintered bodies are expected to be applied as mechanical component materials required for use at high temperatures. A typical example of such a mechanical component is a ceramic gas turbine.
Although a sialon sintered body is excellent in heat resistance and oxidation resistance, it has poor mechanical strength and fracture toughness which lead to a decisive drawback in practical applications. Extensive studies has been made to improve the mechanical strength and fracture toughness of the sialon sintered bodies. Among them all, some of sialon based composite containing SiC fibers in sialons have been developed, as disclosed in Published Unexamined Japanese Patent Application No. 62-12670.
In such a sialon based composite, although the fracture toughness can be improved to some extent, the mechanical strength cannot be sufficiently improved, and improvement on mechanical strength is left unsolved. Strong demand has arisen for further improvements on fracture toughness in practical applications.
Although attempts have been made to improve the mechanical strength and fracture toughness of sialons, a best solution has not yet been found.